As shown in FIGS. 1 and 2, the prior U.S. patent application Ser. No. 08/672,859 of this inventor of the present invention discloses a socket 20 of the socket spanner which has a drive member 21 provided with a square inner hole. The socket 20 further has a driven member 22 provided with a hexagonal inner hole. Located between the drive member 21 and the driven member 22 is a midsection having a center hole 23. The driven member 22 is provided in the inner wall thereof with two grooves 221 opposite to each other. Located near the outer end of the hexagonal hole is a circular slot 222. An elastic body 24 has a retaining side 241 provided with a protruded portion 242, an arcuate bottom 243, and a curved end portion 244. The retaining side 241 can be forced along the groove 221 into the socket 20 such that the end portion 244 is located in the circular slot 222, and that the arcuate bottom 243 can bypass the center hole 23 to move along the outer ring wall. The protruded portion 242 of the retaining side 241 is thus retained securely in the socket 20 at the time when a nut 25 is engaged with the driven member 22 of the socket 20. In the meantime, the end portion 244 of the elastic body 24 urges against the circular slot 222. When the nut 25 is disengaged, the elastic body 24 is thus prevented from slipping out of the socket 20. The elastic body 24 is defective in design in that the end portion 244 of the elastic body 24 is curved to form an angle, thereby making it difficult to force the elastic body 24 into the socket 20.